This invention relates to an air conditioning control system for controlling the cooling and heating of interior and exterior zones of a building, and more particularly to the control of the rejected heat produced by a refrigeration unit located in the building.
In a typical large commercial building having outer offices or areas which have at least one wall exposed to the outdoors and inner offices or areas which have no walls exposed to the outdoors, the interior offices or areas are termed "interior zones" and the outside offices or areas are termed "exterior zones." Such a building normally has an air conditioning system which is capable of delivering cool air by way of interior delivery systems and heated air by way of exterior delivery systems. The interior zones of the building are cooling loads during both winter and summer operation, whereas the exterior zones are heating loads during winter operation and cooling loads during summer operation.
The refrigerating unit in such a building normally comprises a condensor, a compressor and an evaporator. The evaporator chills air conditioning water which is then supplied to, for example, a cooling coil located within the ducts making up the interior delivery system. A fan in the delivery system forces air within the ducts over the cooling coil to lower the temperature of the air and which is then supplied to the zones connected to the ducts. Such air conditioning systems can also include a cooling tower which is located outdoors and through which water circulating through the condensor is passed. Fans in the cooling tower blow air across the water to reject the heat in the water from the building. The air conditioning system may also include a source of fuel heat for heating hot water which is supplied to heating coils located within the duct system. The heating coil then heats air passed over the heating coil by a fan located in the duct. This heated air is then supplied to zones connected to this system of ducts.
The interior zones will all be connected to the cold air ducts whereas the exterior zones are connected to both the cold air ducts and hot air ducts. It has been known in prior art systems to use the rejected heat from the condenser of the refrigerating unit to heat the hot water supplied to the heating coils in the hot air ducts. However, no system has been heretofore disclosed for modulating the chilled water temperature supplied by the evaporator to force the refrigerating unit to produce more rejected heat as a cheaper source of heat than fuel heat.